The Denver APRIL 2016 OBSERVER

M81, the large spiral galaxy at right, and M82, left, in . Visible in small telescopes, this pair lies about 12 million light- from Earth, and about 150,000 light-years from each other. Image © Alan Erickson

APRIL SKIES by Zachary Singer The Solar System If you’re up between 4 and 5 AM, look for the high in Mercury is out of the solar glare, and toward the beginning of the the sky in the south—the familiar scorpion outline looks surprisingly month, it presents a bright, -1 magnitude gibbous disk about 6” across, crowded—and is a wonder on its own, naked-eye. Saturn, Mars, and and low in the west at sunset. As the days progress and the planet or- Antares make a brilliant triangle; Mars and Antares share their hue, bits the Sun, its phase, apparent size and brightness change; maximum but the planet greatly outshines the star. Mars’ apparent diameter will elongation comes on the 18th, when the planet will appear as a “lemon grow to about 16” this month; that’s about as good as it ever gets during wedge” nearly 20° above the horizon at sunset. (On practical basis, less-advantageous op- Mercury will still be more than 10° up that evening when the sky is positions, so these next Sky Calendar dark enough to make observation easier.) Towards the end of the month, weeks are already a 7 New Moon before disappearing in front of the sun, Mercury will become a thin good opportunity for 13 First-Quarter Moon crescent some 10” across, telescopic observa- 21 Full Moon In the Observer but very low on the hori- tion—but we’re not 29 Last-Quarter Moon zon. Those of us in Denver at opposition yet, and President’s Message ...... 2 proper will see the Front next month will be Range as a beautiful com- even better! (Saturn comes to opposition in early June.) Society Directory ...... 2 panion to the innermost Technically speaking, Jupiter is slightly diminished, appearing Schedule of Events...... 2 planet, but folks close to about 7% smaller than last month as Earth speeds away from the giant DAS News ...... 3 the foothills may find their planet after opposition. Realistically, it’s still a stunning object, and at view blocked; if you’re about 41” across, it’s easy for all ’scopes. Jupiter is now a great object About the DAS...... 3 in that group, try heading for kids, because they won’t have to stay up late to see it—look for the NASA Space Place...... 4 eastward for a better line planet in the southeast around 9:30 PM at the beginning of April, and of sight. higher, on the Meridian, at month’s end. Mars and Saturn The Moon continues its recent habit of occulting Aldebaran, this are together in Scorpio! time on April 10th; for observers in southern Denver, the event will occur Continued on Page 6 THE DENVER OBSERVER APRIL 2016

Society Directory PRESIDENT’S MESSAGE by Ron Hranac DAS Executive Board Resources for Learning Astronomy President: Ron Hranac “How can I learn more about astronomy?” president@denverastro .org That question is one that we often hear from our new members and from folks who attend Denver Vice President: Astronomical Society Public Nights and Open Houses. The answer to the question definitely falls into Stuart Hutchins (Interim) vp@denverastro .org the “it depends” category, and might be answered with another question: “What would you like to Secretary: learn?” Jeff Tropeano A good place to start, of course, is with DAS. Our members’ knowledge covers a broad range, and secretary@denverastro .org we love to help others learn more about astronomy. Our monthly meetings at DU’s Olin Hall are a Treasurer: good resource—most feature an astronomy-related lecture. The subject matter can range from entry- Michael Nowak treasurer@denverastro .org level up to college and above. Check out our YouTube page for a sampling: https://www .youtube .com/ Executive Board Members: user/denverastro. Johnny Barela Ed Scholes Our Public Nights (http://www .denverastro .org/das/public-nights/), held every Tuesday and Thurs- Jack Eastman Lindsey Shaw Joe Gafford Ken Sturrock day at DU’s historic Chamberlin Observatory, feature an astronomy-themed lecture followed by ob- Chuck Habenicht Dan Wray serving through the powerful 20-inch Alvan Clark-Saegmuller telescope. (DAS members can attend Past President, Ron Pearson our Open Houses and Public Nights for free.) We also have an area for beginners on our web site at President Emeritus, Larry Brooks http://www .denverastro .org/das/for-beginners/ . Committees Sometimes the area of interest is nothing more than wanting help figuring out how to get the Moon Van Nattan-Hansen Scholarship Fund: or some other object to show up more easily in the eyepiece. (A common gotcha—the telescope’s Jeff Tropeano (Chair) PO Box 100621 finder isn’t aligned with the ’scope!) The first step is to look at the instruction manual, if one is avail- Denver, CO. 80250-0621 able. If the manual is missing, or it isn’t clear about the procedure, bring that ’scope to one of our Open EGK Dark Site Committee: Houses and ask for some hands-on assistance. Darrell Dodge, Interim Chair darksite@denverastro .org After our local telescope shop, S&S Optika, closed (Cathie and Tim Havens retired and moved to New Mexico), DAS member Digby Kirby took over the “how to choose a new telescope” and “how to IDA Representative: Dr. Robert Stencel use your new telescope” presentations normally done around the Christmas holiday season. He plans coloida@hotmail .com to do a couple more of these during the next several months at our Open Houses. Volunteers or Appointed Two magazines that cater to amateur astronomy—Astronomy, and Sky & Telescope—have a wealth Representatives of helpful information for beginners on their respective web sites. On Astronomy magazine’s site : (http://www .astronomy .com), click on the OBSERVING and VIDEOS tabs on the main page. On Sky Darrell Dodge 303 932-1309 & Telescope’s site (http://www .skyandtelescope .com), click on RESOURCES & EDUCATION and Newsletter Editor: Zachary Singer 303 718-4188 Continued on Page 5 editor@denverastro .org Newsletter Proofreaders: DAS SCHEDULE Darrell Dodge, Ron Hranac The Observer is available in color PDF format from the DAS website . Website: Darrell Dodge APRIL 2016 webmaster@denverastro .org IT Coordinator: 8-10 Dark Sky Weekend—EGK Dark Site & Brooks Observatory Ken Sturrock itdept@denverastro .org 16 Open House—DU’s Historic Chamberlin Observatory—Starts at 7:30 PM External Outreach Coordinator: 22 General Meeting at DU’s Olin Hall, Rm. 105, 7:30 PM Julie Candia 29 E-Board Meeting—At DU’s Historic Chamberlin Observatory, 7:30 PM external@denverastro .org Public Night Coordinator: Hugh Davidson 303 679-0629 Librarian: Phil Klos During Open House, volunteer members of the DAS Public Nights feature a presentation on astronomical DAS Information Line: bring their telescopes to the Chamberlin Observa- subjects and a small-group observing session on the (303) 871-5172 tory’s front (south) lawn, so the public can enjoy historic 20-inch telescope (weather permitting), at Cham- DAS Correspondence: views of the stars and planets, try out different berlin Observatory on Tuesday and Thursday evenings Denver Astronomical Society telescope designs, and get advice from DAS mem- (except holidays), beginning at the following times: bers. The Observatory is open, too (costs listed P.O. Box 102738 March 10 - September 30 at 8:30 PM Denver, Colorado 80250 below), and its historic 20-inch telescope is open president@denverastro .org for observing with no reservations necessary. October 1 - March 9 at 7:30 PM Open House costs (non-members): If the skies are clear, Public Night costs (non-members): $4/adult, The Executive Board conducts the business $2/person ($5/family), $1/person in inclement weather. of the DAS at 7:30 PM, at Chamberlin Ob- $3/child and students with ID. DAS mem- DU students with ID, and DAS members free. servatory . bers and DU students with ID: free. Please see the Schedule of Events for meeting Members of the public (non-DAS/DU, as above), please dates . All members are welcome . make reservations via our website http://www .denverastro .org (www .denverastro .org) or call (303) 871-5172.

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Volunteer Opportunities Club Jackets April 10, 7:00AM (setup)-12PM. Maria Torres at (720) 326-1780, or email Dan Wray is taking orders for our black club jackets. The Tabling and, ideally, solar view- mtorres@healthylearningpaths .org . front has your first name embroidered on the right and Denver ing for participants of the 7th An- Astronomical Society printed on the left. The back of the jack- nual Frank Shorter RACE4Kids’ To volunteer, please contact Julie et has the DAS logo printed on it. We are offering both a light Health 5K and Health Odyssey, at Candia at external@denverastro .org weight jacket (essentially, a windbreaker or shell) and heavier the 1st Bank Center in Broomfield. —and thanks! one. It has been some time since we offered the light one. (For questions about the event, contact Prices: light jacket $79, heavy jacket $95; add $4 for sizes ∞ greater than XL—jackets must be paid for in advance. To order yours, send a check made out to “DAS” to Dan Wray, 3970 W. Dartmouth Ave., Denver, CO 80236; let him know the weight of the jacket, size, and the name to be embroidered. Contact: Dan Wray, (303) 922-0905, daniel_wray@comcast .net. (Note that we need to order a minimum of 12 to get a price break, Retaining New Members: New DAS “Ambassador” Position so Dan may hold the order until there are enough to make it a go.) One of the biggest pieces of constructive criticism the DAS received on ∞ our 2015 Membership Survey was that we’re not doing a great job welcom- ing new members into our club: We send a new “welcome” letter, but beyond that, we leave it up to each new member to proactively insert themselves into 30-Meter Telescope Talk the club activities. We must do better, and we need your help to do so. We’ve created a new position in the club leadership: “New Member On Tuesday, April 12th, at 7 PM, Arapahoe Community Col- Ambassador,” and we need it filled! This is an exciting new position—the lege will host Dr. Warren Skidmore’s talk about the Thirty Me- ambassador is going to be the face of the club for new members, and will be ter Telescope project, the scientific drivers for building a giant key to ensuring that new members get welcomed warmly, get introduced to telescope, how the observatory is designed to support a range of the existing members of the club (especially those with similar interests), get scientific studies, and about the engineering solutions that have their questions answered, get signed up for our listserv, learn how to set up been developed to overcome the problems of constructing and a trip to the Dark Sky Site, and so forth…. Since this is a new position, the operating a giant diffraction-limited observatory. responsibilities and day-to-day tasks are really up to whoever fills it! There is no charge, and the talk is targeted to astronomy stu- If you’d like to hear more about this position, or are interested in dents, professionals, and amateur astronomers. The event will be being our New Member Ambassador, please contact Jeff Tropeano: held in Room 3130 on the Main Campus, at 5900 S. jeff .tropeano@icloud .com . ∞ Santa Fe Drive, Littleton. ∞

ABOUT THE DAS Membership in the Denver Astronomical serve Historic Chamberlin Observatory and its Society is open to anyone wishing to join. The telescope in cooperation with the University DAS provides trained volunteers who host of Denver. The DAS is a long-time member educational and public outreach events at the in good standing of the Astronomical League University of Denver’s Historic Chamberlin and the International Dark Sky Association. Observatory, which the DAS helped place on The DAS is a 501 (c)(3) tax-exempt corpo- the National Register of Historic Places. First ration and has established three tax-deductible light at Chamberlin in 1894 was a public night funds: the Van Nattan-Hansen Scholarship of viewing, a tradition the DAS has helped Fund, the DAS General Fund, and the Ed- maintain since its founding in 1952. mund G. Kline Dark Site Fund. The DAS’s mission is to provide its mem- ***JOIN US! More information about DAS bers a forum for increasing and sharing their activities and membership benefits is available knowledge of astronomy, to promote astro- on the DAS website at www .denverastro .org. nomical education to the public, and to pre- ∞ The Denver Astronomical Society One Mile Nearer the Stars Page 3 THE DENVER OBSERVER APRIL 2016 GRAVITATIONAL WAVE ASTRONOMY by Ethan Siegel WILL BE THE NEXT GREAT SCIENTIFIC FRONTIER NASA Space Place

Image credit: Observation of Gravitational Waves from a Binary Black Hole Merger B. P. Abbott et al., (LIGO Scientific Collaboration and Virgo Collabora- tion), Physical Review Letters 116, 061102 (2016). This figure shows the data (top panels) at the Washington and Louisiana LIGO stations, the predicted signal from Einstein's theory (middle panels), and the inferred signals (bottom panels). The signals matched perfectly in both detectors.

Imagine a world very different from our own: permanently shroud- systems—like Earth orbiting the Sun—the waves are so weak that it ed in clouds, where the sky was never seen. Never had anyone seen would take many times the age of the Universe to notice. But when the Sun, the Moon, the stars or planets, until one night, a single bright very massive objects at very short distances, the decay no- object shone through. Imagine that you saw not only a bright point of ticeably and rapidly, producing potentially observable gravitational light against a dark backdrop of sky, but that you could see a banded waves. Systems such as the binary pulsar PSR B1913+16 [the subtlety structure, a ringed system around it and perhaps even a bright satellite: here is that binary pulsars may contain a single neutron star, so it’s best a moon. That’s the magnitude of what LIGO (the Laser Interferometer to be specific], where two neutron stars orbit one another at very short Gravitational-wave Observatory) saw, when it directly detected gravi- distances, had previously shown this phenomenon of orbital decay, but tational waves for the first time. gravitational waves had never been directly detected until now. An unavoidable prediction of Einstein’s General Relativity, grav- When a gravitational wave passes through an object, it simultane- itational waves emerge whenever a mass gets accelerated. For most ously stretches and compresses space along Continued on Page 5

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∞ THE DENVER OBSERVER APRIL 2016

President’s Message Continued from Page 2

the MULTIMEDIA tabs. The magazines are valuable resources, too. Ok, so how does one align a finder with its telescope? Here’s how We often have free copies of back issues available at Chamberlin Ob- I do it: Attach the telescope securely to its mount and tripod, and put a servatory. low-magnification eyepiece—for example, 25 mm focal length—in the If you enjoy learning from books, there are quite a few from which focuser (higher numbers for focal length give you lower power). Sight to choose. Here are some of my favorites: along the telescope barrel as best you can to roughly aim at a distinctive The Backyard Astronomer’s Guide, by Terence Dickinson and Alan target on the ground at least a few hundred feet from you. (Objects in Dyer (Firefly Books, ISBN-13: 978-1554073443). the sky are a poor choice because the Earth’s rotation will cause them Turn Left at Orion: Hundreds of Night Sky Objects to See in a Home to move while you’re trying to align the ’scope, and that can be really Telescope—and How to Find Them, by Guy Consolmagno and Dan M. frustrating!) At twilight or after dark, a brightly lit business sign is a Davis (Cambridge University Press, ISBN-13: 978-0521153973). good option; during the day, look for a stop sign down the street or A Constellation Album, by P.K. Chen (Sky Publishing, ISBN-13: perhaps a chimney on a neighbor’s house. (It may be necessary to ad- 978-1931559386). just the focuser to bring the image into focus.) Center your target in the For a more formal approach to learning astronomy in the greater telescope’s eyepiece—keep in mind that since the ’scope sees a narrow Denver metro area, take a look at the astronomy class offerings from angle even at low power, it may take several tries to aim properly. the likes of Arapahoe Community College, Community College of Au- Next, look through the finderscope or Telrad: If the target isn’t cen- rora, Metropolitan State University of Denver, University of Colorado, tered, adjust the finder until it is (there should be some small screws or and the University of Denver. knobs on the finderscope’s mount, or on the Telrad itself). Recheck the For those who prefer to learn in the comfort of the family room, image in the telescope eyepiece to make sure the object is still centered, DVD-based astronomy courses might be an option. A company called and you should be good to go! The Great Courses (http://www .thegreatcourses .com) sells a wide vari- ety of video-based courses taught by well-known university professors. They have several astronomy courses available, including one that I have at home (Understanding the Universe: An Introduction to Astron- omy, 2nd Edition, by Prof. Alex Filippenko, PhD.). Hint: Look under their sale tab for the best deals. ∞

Gravitational Wave Astronomy

Continued from Page 4

mutually perpendicular directions: first horizontally, then vertically, in Earth was compressed by less than the width of a proton during this an oscillating fashion. The LIGO detectors work by splitting a laser event, yet thanks to LIGO’s incredible precision, we were able to de- beam into perpendicular “arms,” letting the beams reflect back and tect it. At least a handful of these events are expected every . In forth in each arm hundreds of times (for an effective path length of the future, different observatories, such as NANOGrav (which uses hundreds of km.), and then recombining them at a photodetector. The radiotelescopes to detect the delay caused by gravitational waves on interference pattern seen there will shift, predictably, if gravitational pulsar radiation) and the space mission LISA will detect gravitational waves pass through and change the effective path lengths of the arms. waves from supermassive black holes and many other sources. We’ve Over a span of 20 milliseconds on September 14, 2015, both LIGO just seen our first event using a new type of astronomy, and can now detectors (in Louisiana and Washington) saw identical stretching-and- test black holes and gravity like never before. compressing patterns. From that tiny amount of data, scientists were able to conclude that two black holes, of 36 and 29 solar masses apiece, merged together, emitting 5% of their total mass into gravitational wave energy, via Einstein’s E = mc2. During that event, more energy was emitted in gravitational waves than by all the stars in the observable Universe combined. The entire ∞

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∞ THE DENVER OBSERVER APRIL 2016

to Leo

Leo Minor Gemini

Castor

Theta (θ) Canes Venatici Ursae Kappa (κ) Majoris Ursae Majoris Ursa Major NGC 2481 Lynx Phecda Upsilon (υ) Ursae Majoris (The "Big Dipper")

Dubhe Muscida h Ursae Majoris M81

M82

Looking northward from Denver at 9:30 PM in mid-April; deep-sky objects are plotted to mag. 10, and stars to mag. 6. Ursa Major, the Great Bear, appears upside-down when facing north at this date and time, but because the constellation appears to rotate around the north pole (near Polaris, off the chart at bottom), its orientation varies with both time of day and the season.

Object positions, constellation and meridian lines charted in SkySafari, and then enhanced.

April Skies Continued from Page 1 constellation is that nearly all of the Dipper is circumpolar. That is, at at just about 3:52 PM, MDT. For observers in Fort Collins, it takes our latitude and further north, the Dipper never actually sets—though place about 30 seconds later, but to the south in Castle Rock, be ready it may sometimes be low at the northern horizon, it’s always visible 15 seconds earlier. In short, as with the other occultations, don’t rely once the skies get dark (and actually, its stars are up above the horizon on precise times, because they vary somewhat even mile by mile—in even during the daytime). The larger Great Bear extends further south; this case, because the dark limb of the Moon will approach the star in it therefore rises and sets, and is only visible at certain times of year broad daylight, visual estimation of the timing will be all but impos- (although for more of it at our latitude than a very southern constella- sible. Set up and be ready early. tion like Scorpius). For some perspective on this, Xi Ursae Majoris, the bear’s rear foot, is actually a little farther south than Castor, the Deep Sky alpha star of the constellation Gemini. Heading out beyond the solar system this month, we have a trio of To become familiar with Ursa Major, or the Great Bear, start by galaxies—two of which are a good bet that you’ve at least heard of, finding the Dipper—when you see the Dipper “right-side up” (so the even if you haven’t seen them. The third is rather less well-known, would-be contents of its bowl wouldn’t spill out, and the handle is to even by the advanced folks; it should be of interest, though, to all your left), its bowl can also be imagined as the bear’s rear haunches, observers. Before that, we’ll take a quick moment to catch up the new and the handle as the bear’s tail. Extending the lines of the top and bot- folks on the constellation, Ursa Major, or the Great Bear. tom of the bowl about another bowl’s distance westward, you’ll find Most folks are probably more familiar with the Big Dipper, whose another pair of stars, h and Upsilon (υ) Ursae Majoris, that make up famous handle and scoop are easily found in the northern sky. Apart the bear’s shoulder; west of that, the bear’s outline tapers to its “nose,” from the simplicity of the Dipper’s outline (it really does look like a marked by Muscida, or Omicron (ο) Ursae Majoris. giant spoon!), another reason the Dipper is better known than the full Once you’re familiar with the appearance Continued on Page 7

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April Skies Continued from Page 6 of the bear’s body, both on maps and in the sky, you’ll find the bright are also moderately visible in my 12-inch from southern Denver on a stars in the bear’s legs easy to find, since the body will give you the decent night. scale of it all—don’t worry about memorizing them all; just relax and Previously thought to be an irregular galaxy like the Magellanic become familiar with them little by little as you look for objects of Clouds, M82 is now known to be a spiral—but whose structure and interest in their area…. inner workings were greatly altered by interaction with M81 in the Before we get going, then, one last note about Ursa Major on our past. It has prominent dust lanes and intense starburst activity in its map: When you look at the constellation on most sky maps, it sits center, which is pretty unusual in a galaxy like this. It’s also thought “right side up,” with the bear’s feet below it, just north or “above” the constel- lation Leo, the Lion. On our map for this month, though, you’ll see the bear “upside down,” with its feet stick- ing up above it—the reason for this is that the constel- lation is actually north of the zenith (the straight-up point in the sky), so it will be easier to look at it if you turn around and face north to see it, instead of looking southward as we usually do. When you make your 180° “about-face” to the north, the stars there will rotate as you do, and you’ll see them upside down. The constellation also appears to rotate roughly around the North Star, Po- laris, according to the time of day. Since it makes one complete revolution in about 24 hours, you’ll see it shift 90° counterclockwise (when you’re looking north) in 6 hours—the “upside-down” This mosaic image of the magnificent starburst galaxy, Messier 82 (M82) is the sharpest wide-angle view ever obtained bear of 9:30 PM becomes of M82. It is a galaxy remarkable for its webs of shredded clouds and flame-like plumes of glowing hydrogen blasting a “vertical, nose-down/tail- out from its central regions where young stars are being born 10 times faster than they are inside in our Milky Way Galaxy. up” bear in the northwest at 3:30 AM. Image: NASA, ESA and the Hubble Heritage Team STScI/AURA). Acknowledgment: J. Gallagher (University of Wiscon- First up, then, is M81, sin), M. Mountain (STScI) and P. Puxley (NSF). at 9h 56m, +68° 59’. This large, magnitude 6.9 spiral galaxy lies relatively close-by at an esti- that a large number of supernovae are the cause of a high-speed wind mated distance of 12 million light-years. It’s big and bright enough blowing gas and dust outward from this area; the results show clearly to be visible in all telescopes, and in binoculars, too. The inner region in Hubble telescope images. will be seen with careful observation in a 4-inch refractor or a 6-inch To find M81 and 82, follow the imaginary diagonal running roughly reflector, but the spiral arms might remain challenging even in large northwest between Phecda and Dubhe, two of the four stars making instruments. M81 forms the center of a group of galaxies including up the bowl of the Big Dipper. These two stars lie about 10½° apart; nearby M82 (mentioned below), with which it has interacted, and a continuing in the same direction, for nearly the same distance will number of others, like NGC 3077 (46’ to the east-northeast, at 10h bring you to M81—the galaxy should appear in a finderscope. You 5m, +68° 39’). can also “overshoot” about 1½° to d Ursae Majoris, a 4.6-magnitude 2 M82, at 9h 57m, +69° 36’, floats just /3° north of M81 from our star lying on the opposite side of M81 from Dubhe; placing the former point of view, a span that works out to about 150,000 light-years in star near the northwest edge of the finderscope should put M81 near space. This galaxy’s high surface brightness makes it possible to see its center. some structure even with a 6-inch ’scope out in the country; dust lanes Unlike M81 and M82, which are well- Continued on Page 8

The Denver Astronomical Society One Mile Nearer the Stars Page 7 THE DENVER OBSERVER APRIL 2016 April Skies Continued from Page 7 known, but far from bright “land- mark” stars, NGC 2841, at 9h 23m, rd Kappa (κ) +50° 54’, lies between 3 -magnitude Ursae stars Theta (θ) and Kappa (κ) Ur- Majoris Theta (θ) sae Majoris (the latter also known Ursae as Talitha Australis), near the Great Majoris Bear’s front foot. A large spiral gal- axy, about 150,000 light-years across, it’s about half-again larger than the diameter of our own Milky Way. NGC 2481 Measurements of the galaxy’s Ce- pheid variables by the Hubble Tele- scope suggest a distance of about 46 million light-years, or roughly double that of the more familiar Whirlpool Galaxy, M51. In spite of this large distance, NGC 2841 remains quite bright at mag. 9.2, and its inner area is Close-up chart for centering NGC 2481 with a Telrad. Note Theta (θ) Ursae Majoris near east-northeast edge of easily seen in a 6-inch ’scope at about 4° circle, and position of imaginary line between Theta and Kappa (κ) Ursae Majoris relative to the inner and middle Telrad circles. Object positions, constellation and meridian lines charted in SkySafari, and then enhanced. 100X; an 8-inch in good skies may be- gin to show detail in outlying regions. Telrad, towards the east-northeast. A line be- middle (2°) circles—see the close-up chart. To find and center this galaxy, place Theta tween Theta and Kappa should then run about —See you next month. Ursae Majoris near the outer (4°) ring of your halfway between the Telrad’s inner (½°) and ∞

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Denver, Colorado 80250 Colorado Denver,

P.O. Box 102738 102738 Box P.O. The Denver Astronomical Society Astronomical Denver The